Process for the nitration of aromatic hydrocarbons



Patented Sept. 3, 1935 uni-T so STATES 2,012,985 PROCESS FOR THE'NITRATIONOF AROMATIG HYDROGA'RBONS James B. Gastner, woodbnry, N-Ql, assignor'to E. I. du Pontde Ncmours & Company, Wilmington, DeL, a corporation of pelaware NoDrawingr Application September 8; 1932,

' f Serial N0. 632 ,183-

12'Clailiis. (Cl. 260'142) are examples' of such hydrocarbons, from which of. sulfuric and nitric V acids.

the mono, difan'd' tri" nitrocompounds' may be prepared. In the nitration of many of theabove hydrocarbons it is customaryto use as nitrating acids'so-calledmixed' acids, consisting of mixtures In such-mixtures, the sulfuricacid acts, in general, as a dehydrat ing agent, while-the nitric acid brings about the object is such a process in which the nitration of the hydrocarbons is brought about by a nitrat ing acid having a lower content of nitric acid than has been used heretofore. A still further object is such a process for the production of a nitrotoluene. Further objects will appear as the invention is further disclosed hereinafter.

I have found that a satisfactory process for the production of the lower nitro-derivatives of the aromatic hydrocarbons results, if the nitrating acid has a relatively low nitric acid content. While such an acid may be prepared by a simple mixture of the proper proportions of sulfuric and nitric acids, I find that nitroglycerin spent acid, (i. e., the acid remaining after the nitration of glycerin) is very satisfactory for my process. Such nitroglycerin spent acids are available in large quantities at all high explosive plants, and an average composition for a spent acid of this nature may be taken as 75% total H2SO4, 8.5%

. total HNOs, and 16.5% H20.

While various aromatic hydrocarbons are satisfactory for employment according to my invention, such as benzene, toluene, xylene, naphthalene and the like, I find toluene particulary well adapted for the process. Using an acid such as nitroglycerin spent acid, with its low nitric acid content, I find mononitrotoluene to be produced with satisfactory yield, if the proper amounts of toluene andspent acid are used.- After nitration, the nitrotoluene may be separated from the acid byvarious means, for'example-,.by dilution of the mixturewithwater to thepoint where the nitrated' product isinsoluble.

Toluene has a particular advantage in my pro-cesswhen: nitroglycerin spent acid is used,since the toluene serves to" denitratei the acid and to striin it of 1 its" nitric content al'most completely.

While I have found themost desirable results .to ensue when mononitrotoluene is obtained as the product; dinitrotoluene-may alsobe prepared, particularly if the processiscarriedout in two stages where the mononitro derivative is the principal product of thefirst stage." Under certain conditions als -it is satisfactory to p'roduce a mixture of monoand'the dinitrotoluene. It will therefore b"e= apparent 1 that m y" process has great economic advarita'ges; since it allows the use'ofa lowpriced waste acid' tha't is available in large quantities in explosive plants, and brings about the denitration of the waste acid at the same time, a procedure which ordinarily has to be carried out by other and less profitable methods.

When toluene or other aromatic hydrocarbon is nitrated by the process just described, the resulting nitrocompound may contain a certain amount of dissolved nitroglycerin extracted from the acid. The nitrotoluene and any nitroglycerin present after separation from the acid mixture, are washed with water until completely neutral. For the purpose of my invention, the presence of a small amount of nitroglycerin in the nitrotoluene is not only no disadvantage, but is, in fact, an advantage, since this nitrotoluene may be used with satisfactory results as an addition to nitroglycerin for use in dynamites, to improve the freezing properties of the explosive and to bring about other advantages.

As a specific example of the practical adaptation of my process, 500 lbs. of nitroglycerin spent acid, having a composition of approximately total H2804, 8.0% total HNOs or expressed more nearly according to actual composition 75% H2304, 6.0% HNOs, 16.5% H20 and 2.5% nitroglycerin are run into a suitable nitrating vessel. 58 lbs. of toluene are then introduced gradually into the acid with agitation, and cooled, care being taken that an excessive rise of temperature does not result, i. e., not above F. After 30 minutes agitation, the charge is diluted with approximately '75 lbs. of water. The charge is removed from the nitrator and the nitrated material allowed to separate from the acid. The mononitrotoluene is agitated and washed first with hot water, then with sodium bicarbonate soother aliphatic alcohols containing at least two: hydroxyl groups, such, for example as. ethylene glycol. By the term nitroglycerin, I wish to fini-y clude not only that compound by'itself, but the solutions in nitroglycerin of the commonly used freezing point depressants, such as'ethylene gly-' col dinitrate, nitrated polymerized 'glycerin,ni'-' trated sugars, nitrochlorhydrins and the like. gIt; is to be understood that I am'to be limitedonly. as indicated by the following patent claims.

I claim: -1. The process of producing a.;nitrated aromatic hydrocarbon having a small content of a nitrate of an aliphatic alcoholwhich-comprises .nitrating an I aromatic hydrocarbon" with a spent acid resultingfrom the nitration of an aliphatic alcohol containing at least twohydroxygroups and recovering the nitrated hydrocarbonv along with the aliphatic alcohol as a singleproduct.

2. The process "of claim -1, in which thenitration is carried out by means of spent. acid resulting from the nitration of glycerin.

1 3. The process of'claim 1.7. in which thearo matic hydrocarbon is benzene;

. 4. The processor claim.f1,; in which'thearomatic hydrocarbon is xylene s 5. The process of, claim 1, in which the Eartmatic hydrocarbon is toluene. v 5

6. A process which comprises the nitrationof toluene with a spent acid resulting from the nitration or glycerin, dilutingthe acid solution of the nitrocompound with water, and separating from the diluted acid solution the nitrated product together withv the nitroglycerin recovered from the spent acid. V

7. A process for the production of a mononitro toluene containing a small content of nitroglycerin which comprises the nitration of toluene. with'aspent acid resulting irom the-nitration of glycerin, and recovering the nitrated toluene along with the nitroglycerin as a single product.

8. A processfor the production 01a mononitrotoluene whichcomprises the nitration of toluene with a spent acid resulting fromthe nitration'of glycerin, diluting the acid solution of nitrocompound with water, and separating the nitrated "product together with nitroglycerin v re covered from the spent acid.

1; 9..A process for the production of dinitro toluene which comprises the nitration of toluene with *aspent acid resulting from thenitration :of glycerin, and recovering the. nitrated toluene along with the nitroglycerin as a single product. ,10..A process for the 'denitration otynitm glycerinspentflacid which comprises the addition: of an aromatic hydrocarbon thereto. and subseg and recovering at least one of the nitrated -de.-

rivatives of toluene alongwith the nitroglycerin as alsingle product. 12. A processior the denitration or nitro- 

